1. Field of the Invention
The present invention relates to the equalization of audio signals, and in particular to higher resolution control of an equalizer circuit employing multiplying digital-to-analog converters to effect parameter control.
2. Description of the Related Art
Equalizers are commonly used in sound recording environments to alter aspects of the tonality of a recording, and often find themselves incorporated in traditional mixing consoles as part of a channel strip. For instance, sound produced by some instruments may need to be made more prominent, such as that produced by a quiet wind instrument, whilst some may need to be reduced in level, such as that produced by a bass drum. In addition, problems caused by the acoustics of a recording studio, such as an uneven frequency response can be mitigated by using an equalizer.
Equalizers come in a number of flavours. Simple shelving filters boost or cut the level of sound below or above a certain frequency, often called a corner or rollover frequency. Graphic equalizers split an audio signal into a plurality of discrete frequency bands, with gain or attenuation being applied to each individual band. More sophisticated control can be had by employing a parametric equalizer, which allows control of amplitude (gain or attenuation), corner frequency (also known as centre or rollover frequency) and quality factor (Q-factor, or bandwidth) of an audio band. Thus, boost or cut can be applied by varying the amplitude of the band, the frequency it is applied at can be changed by varying the corner frequency, and the frequency range over which equalization is applied can be varied by changing the Q-factor.
Digital control of such equalizers is particularly desirable in recording environments that combine traditional mixing consoles with digital audio workstations (DAWs). A particular parameter can be changed on a DAW, and a corresponding change can be made to that parameter in the equalizer in the mixing console. In addition, adjustment devices on the mixing console itself can be of lower power design, reducing the effects of noise in the system. Problems still exist, however, in enabling higher resolution control of parameters in the equalizer in such digitally-controlled environments, so as to enable fine-tuning at a level offered by analog counterparts.